Social relationships among primates include extensive physical contact between individual members of the relationship. The propensity to seek contact with individuals with which a strong relationship has been established is exemplified in the extreme by the South American titi monkey. These monogamous primates spend up to 90% of their day in physical contact with other members of their family group. Much of the contact between family members is passive -animals sit side-by-side with their lateral surface in close contact with another monkey. A unique aspect of this social contact is tail-twining. As animals sit in passive contact, they swing their tails laterally until it contacts the other animal's tail and then the tails tightly wrap around one another. When multiple animals are sitting together they wrap all of their tails in a single tail- twine. Active contact between titi monkeys includes grooming, grasping an arm to pull adjacent animals closer, nuzzling the chest or mouth of another group member, and, for males, bimanual clasping of the female's haunches during copulation. The proposed research will examine the role of several somatosensory cortical areas we believe are involved in the expression and maintenance of affective social relationships. We will examine information processing and the functional organization of somatosensory areas in anterior and posterior parietal cortex using multiunit recording techniques and neuroanatomical tracing techniques. We expect that representation of body parts, involved in social contact, will be magnified compared to other primates. We will selectively lesion, using aspiration techniques, different cortical fields in animals from well-established social groups. We will then monitor changes in social behavior and social motivation associated with the loss of a specific field or body part representation therein. These studies are unique in that they take advantage of an overt behavior, directly mediated by the somatosensory system, to examine the role of cortical mechanisms involved in discrete social interactions.